1. Enterprise JavaBeans
Ruslana Svidzinska
CSE690

2. What is EJB?
q An EJB is a specialized, non-visual
JavaBean that runs on a server.
q EJB technology supports application
development based on a multiplier,
distributed object architecture in which
most of application’s logic is moved
from the client to the server.

3. Server Components
q Server components are application
components that run in an application
server.

4. Java Application Servers
q A Java application server provides an
optimized execution environment for
server-side Java application
components.
q A Java application server delivers a
high-performance, highly scalable,
robust execution environment
specifically suited to support Internet
enabled application systems.

5. WORA
q The Enterprise JavaBeans architecture
defines a standard model for Java
application servers to support “Write
Once, Run Anywhere” (WORA)
portability

6. Component Portability
EJB technology takes the WORA concept
to a new level.
EJB completely portable across any
vendor’s EJB compliant application
server. The EJB environment
automatically maps the component to
the underlying vendor-specific
infrastructure services.

7. Overview of EJB Technology
EJB Component Model
Enterprise JavaBeans component model logically
extends the JavaBeans component model to
support server component.
Server components are reusable, prepackaged
pieces of application functionality that are
designed to run in an application server.
EJB can be assembled and customized at
deployment time using tools provided by an EJB-
compliant Java application server.

8. Simplifying Development.
The EJB architecture provides an
integrated application framework.
An EJB server automatically manages a
number of tricky middleware services on
behalf of the application components.
EJB component-builders can concentrate
on writing business logic rather than
complex middleware

9. Simplifying Development (cont’d)
RESULT:
•Application get developed more quickly
•Code is of better quality.

10. What EJB Accomplishes
You can take any Java class and with little effort make
it a distributed, secure, transactional class
You can take any data source and make the data
source appear to be a collection of Java objects
– Eliminates distinction between data from a
database and any other source
– All information is accessed through Java objects
– All SQL is cleanly encapsulated in Java objects
q true object-oriented programming
q high reusability
– Database objects work with the full Java class

11. What EJB Means to Us
q Developers can focus on writing business logic
rather than writing low-level infrastructure like data
access, concurrency, transactions, threading, etc.
– Reduces development time
– Reduces complexity
– Increases quality and reliability
q The knowledge about EJB is portable among
many different products because EJB products are
based on a common standard
q Greater reuse because code is located in shareable,
server objects

12. So....let’s take a look at
Enterprise JavaBeans
5 A specification from JavaSoft
5 Enterprise JavaBeans defines a server component
model for the development and deployment of Java
applications based on a multi-tier, distributed object
architecture
5 The Enterprise JavaBeans specification defines:
– A container model
– A definition of the services the container needs to
provide to an Enterprise JavaBean, and vice versa
– How a container should manage Enterprise
JavaBeans

13. Enterprise JavaBeans
Architecture
The EJB architecture specifies the
responsibilities and interactions among
EJB entities
 EJB Servers  EJB Containers
 Enterprise Beans  EJB Clients
Enterprise Enterprise
Bean Bean
EJB Container
Clients
EJB Server

14. EJB Server
Provides a Runtime Environment
q The EJB Server provides system services and
manages resources
– Process and thread management
– System resources management
– Database connection pooling and caching
– Management API
EJB Server

15. EJB Container
Provides a Run-time Environment
for an Enterprise Bean
q Hosts the Enterprise JavaBeans
q Provides services to Enterprise JavaBeans
– Naming
– Life cycle management
– Persistence (state management)
– Transaction Management
– Security
q Likely provided by server vendor
EJB Container
EJB Server

16. Enterprise JavaBeans
q A specialized Java class where the real business logic
lives
– May be developer-written or tool-generated
q Distributed over a network
q Transactional
q Secure
q Server vendors provide tools that automatically
generate distribution, transaction and security
behavior Enterprise Enterprise
Bean Bean
EJB Container
EJB Server

17. EJB Clients
q Client access is controlled by the container in
which the enterprise Bean is deployed
q Clients locates an Enterprise JavaBean through
Java Naming and Directory Interface (JNDI)
q RMI is the standard method for accessing a bean
over a network
Enterprise Enterprise
Bean Bean
EJB Container
Clients
EJB Server

18. What’s Unique About EJB
Declarative Programming Model
q Mandates a container model where common services are
declared, not programmed
– At development and/or deployment time, attributes defining
the bean’s transaction and security characteristics are
specified
– At deployment time, the container introspects the Enterprise
JavaBean attributes for the runtime services it requires and
wraps the bean with the required functionality
– At runtime, the container intercepts all calls to the object
y Provides transactional, threading and security behavior
required before the method invocation
y Invokes the method on the object
y Cleans up after the call

19. Understanding EJB Components

20. JavaBeans vs Enterprise
JavaBeans
q Enterprise JavaBeans is a framework for
building and deploying server-side Java
components
q JavaBeans is a framework for client-side Java
components
q Conceptually related because both are
components
q The specifications are different
q The specifications do not build on each other
or rely on each other

21. What’s in the EJB Specification
~200 Pages of technical material for EJB vendors
q Goals for the Release
q Roles and Scenarios
q Fundamentals (Scope of EJB)
q Session and Entity Beans
q Transactions, Exceptions, Distribution
q EJB Bean and Container Responsibilities
q API Reference
EJB Vendors
Have to do all the WORK

22. Enterprise EJB Scenario Existing
Enterprise
Middleware
EJB Application
Clients Web Server
Server
CICS Programs
Browser EJB Container
Credit Card
Servlet Shopping
Databases
Cart
Inventory
Application
SAP Modules
EJB Server

23. An inside look at the various
components of EJB
q Bean Class is written by the developer
q EJBHome and EJBObject interfaces and classes
control access to the Bean class EJB Container
q Deployment Descriptor
EJBHome
EJBHome
Interface
and MANIFEST describe
Class
security and transactional
characteristics of the Bean EJB Class
EJBObject
EJBObject
Interface
Class
Written by Developer
Generated at Development
Generated at Deployment
Deployment
Manifest
Descriptor
EJB Server

24. EJBHome Interface and Class
q Used to get a reference to a bean’s remote interface
q Provides bean creation services
– myFoo = fooHome.create() instead of
myFoo = new foo()
– Supports multiple signatures to create EJB instances
q Similar to class factory EJB Container
in COM and CORBA
EJBHome
EJBHome
Interface
May be generated by
Class
q
tools that come with an
EJB server
q Also manages EJB:
– querying (Entity Bean)
– deleting (Entity Bean)
EJB Server

25. Interface javax.ejb.EJBHome
q Home objects must implement this interface
q Returns a reference to a bean by creating or finding
it
q Every bean has a EJBHome interface that provides
methods for getting references to one or more beans
– create methods are used to create new beans
– there can be many create methods, similar to a
class having many constructors
q Provides a bean removal interface also
q The EJBHome Class implementation is provided by
the EJB Server Provider

26. Sample EJBHome Interface
public interface CustomerHome extends EJBHome
{
public abstract Customer create(String id, String name)
throws RemoteException, CreateException;
public abstract Enumeration findByName(String val)
throws RemoteException, FinderException;
public abstract RemoteEnumeration findStateByName(String val)
throws RemoteException, FinderException;
public abstract Customer findByPrimaryKey(CustomerKey pkey)
throws RemoteException, FinderException;
public abstract Customer findByPrimaryKey(CustomerKey pkey, int findSource)
throws RemoteException, FinderException;
public abstract CustomerState findStateByPrimaryKey(CustomerKey pkey, int
findSource)
throws RemoteException, FinderException;
}

27. Client makes invocation to EJBHome
Class via the EJBHome Interface
q Client calls one of the create() methods on the
EJBHome Class. The EJBHome class can have
multiple create() signatures.
EJB Container
EJBHome
Class
create()
Clients
EJB Server

28. EJBHome Class instantiates
the Bean Class
q When the create() method is
called in the EJBHome Class, it
is responsible for instantiating
the Bean class. EJB Container
EJBHome
Class
EJB
Class
Clients
EJB Server

29. EJBObject Interface and Class
q Intercepts calls to the EJB Class to add support for:
– transactions
– security
– threading EJB Container
q EJBObject class has the same methods
as the bean and delegates to the bean
for actual behavior
q EJBObject class checks security and
EJBObject
EJBObject
sets up transaction before delegating
Interface
Class
method call to the bean
q Clients can never get a reference to
a bean’s EJB Class, only the EJBObject
interface EJB Server

30. Interface javax.ejb.EJBObject
public interface javax.ejb.EJBObject extends java.rmi.Remote
{
EJBHome getEJBHome() throws RemoteException;
Handle getHandle() throws RemoteException;
Object getPrimaryKey() throws RemoteException;
boolean isIdentical(EJBObject obj) throws RemoteException;
void remove() throws RemoteException, RemoveException;
}
q Represents a specific bean instance
q Remote objects must implement this interface
q Primary key is an object that represents the primary
key for a specific instance of a bean
q The EJBObject Class implementation is
provided by the EJB Server Provider

31. Sample EJBObject Interface
public interface Customer extends EJBObject
{
public abstract String getId() throws RemoteException;
public abstract String getName() throws RemoteException;
public abstract void setName(String val) throws RemoteException;
public abstract boolean getNameNull() throws RemoteException;
public abstract boolean getIdNull() throws RemoteException;
public abstract Enumeration getAccounts() throws RemoteException;
public abstract void addToAccounts(Account relInst) throws RemoteException;
public abstract void removeFromAccounts(Account relInst)
throws RemoteException;
}

32. After the EJBHome Class
instantiates the Bean...
q The EJBHome Class will instantiate the EJBObject Class,
initializing it with the remote object reference to the Bean
Class.
q The Client will now EJB Container
communicate to the
EJBHome
EJBObject Class.
Class
Passes ref
The EJBObject Class of Bean
will delegate the call to
the Bean.
EJBHome
Class
Client now has reference EJB
Clients to the EJBObject Class.
Class
NOT A REFERENCE
TO THE BEAN
ITSELF!!!! EJB Server

33. Client communicates to the Bean
class via the EJBObject Class
q Client never has a direct reference
to the Bean.
q The EJBObject Interface is the
EJB Container
interface for the Bean, so the
EJBObject Class “delegates” the
EJBHome
calls to the Bean.
Class
q The EJBObject Class
implementation will be
generated using vendor
tools.
EJBHome
Class
EJB
Class
Clients
EJB Server

34. EJB Class
q A bean has a single Java class at its core
– This class is written by a developer if it’s a session
bean
– This class is sometimes generated by a tool if it’s an
entity bean
q Implements application-specific business logic
q Implements one of the following contracts:
– javax.ejb.EntityBean
– javax.ejb.SessionBean
q These contracts provide for consistent behavior when
activating beans, passivating beans, reading data,
writing data
q Every container can expect these methods in every bean

35. Deployment Descriptor
q Allows you to declare transaction and security attributes,
NO PROGRAMMING REQUIRED!!!
q An EJB Deployment Descriptor describes the classes,
interfaces and declarative behavior of an EJB
q Deployment Descriptor format is serialized objects:
– javax.ejb.deployment.ControlDescriptor
– javax.ejb.deployment.DeploymentDescriptor
– javax.ejb.deployment.EntityDescriptor
–
EJB Container
javax.ejb.deployment.SessionDescriptor
q The deployment descriptor
is generated by server tools
The deployment descriptor
Deployment
q Descriptor
classes are defined in the EJB Server
EJB specification

36. Let’s look at the value of the
Deployment Descriptor
q Step #1 - Write your Bean implementation.
q Step #2 - Compile this Java source into Java bytecode
q Step #3 - Developer is responsible for creating a
serialized deployment descriptor for the bean. Most
likely using a tool from the vendor. EJB tools will use
Reflection API on the compiled EJB Bean to determine:
– name of Bean class
– methods
– parameters
– return values
q Step #4 - The EJB Tool will use the above information to
generate a Deployment Descriptor file and an editor
with which to set transaction and security attributes.

37. Sample Contents of a
Deployment Descriptor
PS(TicketDemo,Concert,deployment_descriptor)
Entity{
VersionNumber
{
1.0
}
BeanHomeName
{
ConcertHome
}
ControlDescriptor
{
IsolationLevel
{
TRANSACTION_READ_COMMITTED
}
Method Level Method
Security Attribute {
int getId() throws java.rmi.RemoteException
}
RunAsMode
{
Method Level SYSTEM_IDENTITY
}
Transaction Attribute
TransactionAttribute
{
TX_SUPPORTS
}

38. Enterprise JavaBean Packaging
q Enterprise JavaBeans are comprised of many Java files
q These files are put in a JAR file
– A JAR file is a ZIP file with a MANIFEST that
describes the contents of the file
– A MANIFEST is a simple text file
q Name: bank/AccountDeployment.ser
Enterprise-Bean: True
q A JAR file can contain more than one Enterprise
JavaBean
EJB Container
Manifest
EJB Server

39. Bean Development Process
q Implement the EJB Class
q Specify the remote interface
EJB Container
q Specify the home interface
Specify security and
EJBHome
EJBHome
Interface
q
Class
transactional characteristics
using vendor tools
(DeploymentDescriptor) EJB Class
Use vendor tools to
EJBObject
EJBObject
q
Interface
Class
generate supporting
code and package
components in EJB-jar
q Iterate... Written by Developer
Deployment
Manifest
Generated at Development Descriptor
Generated at Deployment EJB Server

40. Enterprise Beans:
Session Beans & Entity Beans
Session Beans vs. Entity Beans
Bean-Managed Persistence
Container-Managed Persistence
EJB Transaction Attributes

41. Comparing Session and Entity
Beans
Session Beans Entity Beans
q Optional for EJB 1.0
q Mandatory for EJB
q Represents
1.0
underlying data
q Represents a specific object or context
client (clients share instance)
(1 instance per client) q Long-lived
q Short-lived q Persistent
q Transient q Can be a class that
q Can be any Java maps to persistent
data
class (e.g., database)
q May be transactional q Always transactional
q Business Logic Beans q Beans which

42. Session Beans
Represents Process
q A transient agent for an individual client that
executes on a server (e.g., ShoppingCart)
q Session beans are often a client of multiple entity
beans
q Implements javax.ejb.SessionBean interface
q State management types for session EJBs
– stateful - session bean may maintain state information
across method calls
– stateless - session bean may be used to service multiple
clients
– a stateless session bean can only have a single no-argument
create() method in its Home interface

43. Session Beans - Stateful or
Stateless
q A Stateful Session Bean maintains a one-to-one relationship
with a Client. It maintains a user “session”. Most common
example is an e-commerce application with a “shopping cart”
unique for each user.
– Container will automatically “swap out” the Session bean if it is inactive. Here
the container calls the ejbPassivate() method to save any private data to some
physical storage.
– When container receives new request, the Container will call the ejbActivate()
method to restore the Session Bean.
q A Stateless Session Bean can be accessed by multiple incoming
clients and keeps no private data. It does not maintain a
unique session with a client.
– Keeps no persistent data. If it crashes, container simply starts another one and
the client transparently connects.
– All access to the Bean is serialized.

44. Entity Bean
Represents Data
q Implements javax.ejb.EntityBean interface
q Maps a data source to a Java class
– table, view, join or stored procedure in a relational database
– a set of related records in a database
– legacy data
q Each instance of an entity bean is one row of data
q Each instance of an entity bean is uniquely identified
by a primary key
q An Entity Bean can also have additional methods for
business logic, etc.

45. Defining an Entity Bean
q An Entity Bean must implement the
javax.ejb.EntityBean interface. In addition, the Entity
Bean must implement an ejbCreate() method for
each create() method on the Home Interface.
q When the Home class gets a call to create(), it calls
the ejbCreate() method on the Entity Bean with the
corresponding signature.
q ejbStore() and ejbLoad() used to synchronize Entity
Bean data with the database.
q ejbActivate() and ejbPassivate() used for notification
that Entity Bean state is being written to the
database or restored from the database.

46. Since Entity Beans represent
Data...
q Each instance of an Entity Bean is
uniquely identified by a primary key
object
q Primary key can be saved and used
later to regain access to the same EJB
object identity
– fooKey = fooBean.getPrimaryKey();
…
fooBean =
fooHome.findByPrimaryKey(fooKey);

47. Entity Bean Operations
q BeanHome.create() is equivalent to an SQL INSERT
– Causes a new database record to be inserted into
the database:
q customerBean = customerHome.create(”Jane",
”Rodgers");
q BeanHome.findSomething() is equivalent to an SQL
SELECT
– Creates a bean instance that represents queried data from
a database
– Can also return an enumeration to represent multiple rows
of data
q There will typically be many findSomething() methods:
q customerBean =
customerHome.findByName(firstName, lastName);
q customerBeans = customerHome.findByZip(94023);

48. Entity Bean Operations
q BeanHome.remove() and EJBObject.remove()
are equivalent to an SQL DELETE
– causes the database record to be deleted from the
database
q customerBean = customerHome.findByName(“Jane”,
“Rodgers”);
customerBean.remove();
q Commiting a change on a found object is
equivalent to an SQL UPDATE
q customerBean = customerHome.findByName(“Jane”,
“Rodgers”);
customerBean.setEmailAddress(“jane.rodgers@yahoo.
com”);

49. EJB Persistence
q Provides Entity Beans the ability to
store and retrieve their state
q Can be implemented by a bean
– Bean Managed Persistence
q Can be implemented by a container
– Container Managed Persistence

50. Bean Managed Persistence
q The entity bean is responsible for its persistent
behavior
q EJB developer must implement database access
– ejbCreate(…), ejbLoad(), ejbStore(), ejbRemove()
q Not automated, developer manually creates mapping
through JDBC calls
q Not as reusable
– Hard-code database access within class
q Advanced features like connection pooling and
caching are difficult to support because of reliance on
hand written code

51. Container Managed Persistence
q The EJB container is responsible for
persistence
q The container provides tools that generate
code in the EJB class that maps methods in
the bean to a result set
– Can map to a table, view, join or stored procedure in a
database
– Server provides automated mapping to convert relational
data to bean instances
q Advanced features like connection pooling
and caching are easily supported
q High reuse

52. EJB Transaction Support
q EJB allows you to either DECLARE transactions or CODE
THEM EXPLICITLY.
– TO DECLARE: EJB allows you to declare transaction
support in the Deployment Descriptor and then have the
container take care of the details inside the remote class
q Transaction attributes specified at the bean and method level
– FOR EXPLICIT CONTROL: An EJB Container is required
to implement javax.transaction.UserTransaction
q Provides an interface to a transaction service
q Can be used by EJB clients and enterprise beans that are declared
to manage their own transactions (TX_BEAN_MANAGED)
– EJB specification does not support nested transactions

53. EJB Transaction Attributes
q TX_NOT_SUPPORTED
– Cannot execute within a transaction
– Suspends any existing transaction while method is called
q TX_SUPPORTS
– Executes with or without a transaction
– Doesn’t suspend existing transaction
q TX_REQUIRED
– Executes within a transaction
– If no transaction exists, starts a new one and commits it when method completes
q TX_REQUIRES_NEW
– Always starts a new transaction and commits it when method completes
– Suspends existing transaction
q TX_BEAN_MANAGED
– The bean manages its own transaction control
– Suspends existing transaction
q TX_MANDATORY
– Must execute within a transaction
– If no transaction exists, throws the TransactionRequiredException